Thixotropic gelled bipropellant composition containing sulphated galactose polymer



United States Patent O 3,470,042 THIXOTROPIC GELLED BIPROPELLANT COM- POSITION CONTAINING SULPHATED GA- LACTOSE POLYMER Chester J. Grelecki, Rockaway, Robert A. Keeler, Denville, and Barna Szabo, .lr., Elizabeth, N.J., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy N Drawing. Filed Feb. 24, 1967, Ser. No. 619,128 Int. Cl. C06b 17/00, 19/04; C] 7/02 US. Cl. 149-22 10 Claims ABSTRACT OF THE DISCLOSURE A gelled bipropellant composition wherein the gelling agent is a Sulphated galactose polymer.

BACKGROUND OF THE INVENTION This invention relates generally to propellants and more particularly to a gelled high energy bipropellant which is suitable for use in rockets, missiles, torpedoes and the like.

In general propellants are divided into two types: monopropellants and bipropellants. The monopropellant is characterized by a single phase containing both fuel and oxidant. Although this combination may be a physical admixture, the oxidant may in fact be combined with the fuel in a single material, or in some instances in a single molecule. The bipropellant, conversely, is characterized by a separation of the fuel and the oxidant. In practice, each is physically and separately stored until the moment of detonation. As used herein, the term bipropellant refers only to the fuel component and its additives which, composition must be contacted with an oxidant for combustion.

Gelled bipropellant compositions per se are well known in the art and are desired for their combination of the most advantageous properties of solid and liquid propellants. Hence, the gelled propellant combines the safety, storability and transportability of the solid propellant, with the ease of handling and burning rate control obtainable with the liquid propellant. Moreover, the gelled propellant unlike the solid material, can be easily pumped through small orifices like liquids, but without the consequent foaming problem normally associated with liquid handling. The gelled propellant also possesses the added safety features of the solid propellant in that it will not spill due to accidental rupture or perforation of storage tanks or feed-lines, nor will it tend to slosh within the fuel tanks during rocket flight which may adversely affect flight stability.

Heretofore, gelling agents for liquid fuels have failed to meet the stringent requirements of rocket and missile vehicles in that satisfactory gels could not be formed by simple stirring or mixing with reasonable quantities of gelling agent within a reasonable length of time. Moreover, prior art gelling agents such as Jaguar gum, cellulose gum, Kelcosol, and Methocel have been found to suffer from a tendency to separate out overnight or to form a gummy or otherwise difficult to handle product. Further,

3,470,042 Patented Sept. 30, 1969 ice the Carbopol gelling agents, such as those disclosed in US. Patent No. 3,232,801, while overcoming, to some extent these prior art problems, have been found to be highly sensitive to air and carbon dioxide contamination and hence incapable of being prepared under conditions of high shear mixing in the presence of a normal air atmosphere.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a gelled bipropellant composition which is both mechanically and thermally stable and which may be prepared under conditions of high shear mixing in the presence of a normal air mixture.

Another object of this invention is to provide a mechanically stable gel composition capable of suspending a relatively large percentage of powdered metal or metal hydride while exhibiting only a negligible tendency to settle even after extended periods.

Briefly, in accordance with the invention, the above and other objects are obtained by providing a gelled bipropellant composition wherein a sulfated galactose polymer is used as the gelling agent.

DESCRIPTION OF PREFERRED EMBODIMENT Sulphated galactose polymers are obtained by refining water soluble carrageenin which is extracted from marine plants. It is a polysaccharide composed of 3,6 anhydro-dgalactose and sulfated d-galactose residues, linked together to form a long chain polymer having a molecular weight of up to several hundred thousand. Among the preferred gelling agents of this invention are those sold under the names of Gelcarin DG and Gelcarin HWG which are trademarks of the Marine Colloids Inc., Springfield, NJ.

It has now been found that a mechanically stable gelled bipropellant is obtained by admixing a fuel component with the sulfated galactose polymer in an amount sufficient to cause thioxotropic gellation. Preferably 0.5 to about 20% based on the weight of said fuel composition may be used depending on the type of fuel being gelled. More preferably, however, an amount of from about 1-5 percent based on the weight of the fuel composition is usually effective. It should be understood that greater amounts of gelling agents may also be employed although such is normally to be avoided since the gelling agents of this invention are completely eliective at the low concentrations and additional gelling agent is of no further benefit.

Any liquid fuel component may be used which can be gelled by the sulphated galactose polymer, but in general it has been found that only those fuels which are water soluble give best results. Of these the most preferred are mixtures containing at least one compound from the group selected from wherein each R is selected from the group of H, lower alkyl, phenyl or methylphenyl,

wherein each R is selected from the group consisting of H and lower alkyl and wherein m is a number rang ng from to 4, alcohols selected from the group consisting of furfuryl alcohol, ethyl alcohol and isopropyl alcohol, and mixtures thereof.

Among those specifically preferred are liquid ammonia, aniline, ethylamine, methylamine, ethylene diamine, o-toluidine, triethylamine, hydrazine, unsymmetrical dimethyl hydrazine, monomethyl hydrazine, dimethylenetriamine, furfuryl alcohol, ethyl alcohol, isopropyl alcohol, and mixtures of any of the above such as for example, mixtures of -20 parts hydrazine with 80-100 parts monomethyl hydrazine.

There may also be included as an optional ingredlent, powdered metals such as aluminum, beryllium, magnesium, boron, zirconium, titanium and the hydrides thereof and also aluminum borohydride. The metals and metal hydrides possess the advantages of increasing density and improving specific impulse because of their high heat of combustion. The amount of powdered metal added is not critical but is determined largely by specific use and the requisite physical characteristics of the composition. Even very minor additions as 1-2% by weight will increase density and heat of combustion, however one of the important features of this invention is that significantly greater amounts of the powdered metal can be suspended in the gelled fuel without any undesirable settling out.

Particle size of the powdered metal is not critical when employing the gelling agents of this invention. Preferably 4 Example 6 Parts Gelcarin HWG 2 Beryllium powder I-Iydrazine 68 The resultant gels were then tested for thermal stability and compared with Carbopol 940.

TABLE I.THERMAL STABILITY OF GELS Test Stability, gas tempera- Test evolution (cc. ture duration gas) lb. of Gel composition F.) (days) gel/min.

Neat gels:

2.5% DGINzH4 Ambient 30 6X10- 160 30 6X10- 2.0% HW GIN 2H4 Ambient 30 6X10- 16 30 12X10- 1% DG, 1.5% HWG/N2H4 Ambient 30 6 10- 160 30 6Xl0- 940IN2H4 Ambient 30 6X10' 160 30 15x10" Aluminum loaded gels:

2.5% DG/% Al/N2H4. Ambient 30 6X10 160 30 6X10- 2.0% HWG/40% Al/NzH-.. Ambient 30 1. 2X10- 160 30 6X10 1.0% DG, 1.5% HWGI40% Ambient 3O 4X10- /NzH4. 160 30 4X10- 940/40% Al/N2H4 Ambient 30 1. 5X10a 160 30 21Xl0-a The above formulated gels were also aged for 2 to 25 days after and subjected to an acceleration of 18 gs for varying periods of time to test for gel viscosity and separation as a function of age.

TABLE II.GEL VISCOSITY AND AggEgEgtATION TESTS AS A FUNCTION Gel composition (Wt. percent) Age (days) Acceleration test, liquid separation (wt. percent) Apparent Viscosity (poise) at 100 see- Gelcarin, Al-N2H42 the metal is in a finely divided form, however, having a particle size of less than about microns.

Other additives can also optionally be suspended or dissolved therein for example, burning rate catalysts such as ferrocene and the like.

In general, the gelled bipropellants of this invention are prepared by mixing from about 0.5-5 parts of a high molecular Weight sulphated galactose polymer with about -100 parts of a fuel composition as hereinabove mentioned, such as hydrazine. Optionally from about 10-63 parts of a powdered metal or metal hydride such as aluminum powder may be suspended therein. Preferably, the components of the mixture are mixed under conditions of high shear for periods of time ranging from about 3 to 10 minutes.

The foregoing invention is further illustrated by the following examples which are presented for purposes of illustration only and should not be regarded as limitative in an way.

EXAMPLES The following formulations were prepared by agitating the mixture under high shear conditions with a duplex laboratory dispersator unit for periods of 3-10 minutes. All formulations are in parts by weight.

Aluminum Example Hydrazine powder Gelcarin H G Gelcarin D G Similar results are obtained with liquid ammonia, aniline, triethylamine and mixtures containing 16% hydrazine and 84% monomethyl hydrazine, also furfuryl alcohol.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A gelled bipropellant composition comprising the mixture of a liquid water soluble fuel composition devoid of combustible combined oxygen, requiring an external oxidizer for combustion, and selected from at least one compound from the group consisting of:

wherein each -R is selected from the group consisting of H, lower alkyl, phenyl and methyl-phenyl,

wherein each R is selected from the group consisting of H, and lower alkyl and wherein n is a number ranging from 0 to 4, alcohols selected from the group consisting of furfuryl alcohol, ethyl alcohol and isopropyl alcohol, and mixtures thereof; and a gelling agent comprising a polysaccharide containing 3,6-anhydro-d-galactose and sulfated d-galactose residues in 'an amount sufiicient to cause thioxtropic gelation.

2. The bipropellant composition of claim 1 wherein at least a portion of said fuel composition comprises a hydrazine compound.

3. The bipropellant composition of claim 2 wherein said fuel composition comprises a mixture of -20 parts of hydrazine with 80 100 parts of monomethyl hydrazine.

4. The bipropellant composition of claim 1 wherein said fuel composition comprises tirethylamine.

5. The bipropellant composition of claim 1 wherein said fuel composition comprises furfuryl alcohol.

6. A gelled bipropellant composition comprising the mixture of a liquid water soluble fuel composition devoid of combustible combined oxygen, requiring 'an external oxidizer for combustion, and selected from at least one compound from the group consisting of:

wherein each R is selected from the group consisting of H, lower alkyl, phenyl and methyl phenyl,

wherein each R is selected from the group consisting of H, and lower alkyl and wherein n is a number ranging from 0 to 4, alcohols selected from the group consisting of furfuryl alcohol, ethyl alcohol and isopropyl alcohol, and mixtures thereof; a gelling agent comprising a polysaccharide containing 3,6-anhydro-d-galactose and sulfated d-galactose residues and having a molecular weight of up to several hundred thousand in an amount suflicient to cause thixotropic gelation; and from about 20 to about 60 percent by weight of a powdered metal suspended therein said composition.

7. The bipropellant of claim 6 wherein the powdered metal is selected from the group consisting of aluminum, beryllium, magnesium, boron, zirconium, titanium and the hydrides thereof.

8. The bipropellant composition of claim 1 wherein the gelling agent is present in an effective amount of from about 1 to 5 percent based on the weight of said fuel composition.

9. A gelled high energy bipropellant comprising the mixture of -l00 parts of a hydrazine compound with from about 0.5-5 parts of a high molecular weight sulphated galactose polymer and from about 10-63 parts of aluminum powder suspended therein.

10.The bipropellant of claim 8 wherein a minor amount of a burning rate catalyst is dispersed therein.

References Cited UNITED STATES PATENTS 2,951,335 9/1960 Stengel 149-36 3,116,187 12/1963 Scaulon et a1. l4936 X 3,197,348 7/1965 Skolnik l49l8 3,232,801 2/1966 Bost et a1. l49l9 3,242,020 3/ 1966 Atkins 149-44 X 3,326,733 6/1967 Colgrove 149-44 X 3,334,053 8/1967 Audrieth l49l8 X 3,359,144 12/1967 Atkins et a1. l49l8 X BENJAMIN R. PADGETI, Primary Examiner U.S. Cl. X.R. 

